Inflatable packers of varying design have been in use downhole. When the downhole thermal conditions are fairly stable, there is a negligible effect on the inflated pressure of the elastic sealing element. If, however, after inflation, the surrounding temperature of the well fluids increases, the thermal loads applied to the fluid within the expanded element increase as the pressure rises in response to fluid expansion. While some tolerance can be built into the design, the temperature gradient can become sufficiently severe in an upward direction so as to cause sufficient incremental pressure in the inflated element to cause it to burst. In the other direction, where the temperature of the surrounding well fluids cycles downwardly, a resulting decrease in internal pressure is experienced within the inflated element and, depending on the circumstances and the severity, a loss of sealing and anchoring engagement of the packer or bridge plug with the casing wall can occur.
Prior designs have emphasized relief of excess pressure by allowing fluid from inside the element to escape into the well fluids upon a rise in internal pressure within the element beyond a predetermined level less than the failure pressure of the element.
Accordingly, one of the objects of the present invention is to provide a compensation system that responds to a rise or a fall or cycling involving rises and falls in temperature and compensates for the thermal effects by respectively allowing fluid to be removed from under the inflated element or adding fluid to the space under the element. Another object of the present invention is to provide a system that compensates for increases and decreases in thermally induced pressure loads, while at the same time isolating the compensation system from wellbore fluids.